Your bigger than the average boy or man. Wearing and jerking into panties is rare but you're not alone. But as long as you're not hurting anybody and you're not addicted to it, whatever. But I'd say u kinda are hurting your aunt by stealing her property.

You are really big for your age. Well done. I was seven inches at 14 before I shrunk to a more stable size of 6 haha. The underwear is something I cannot say. I almost stole my cousins undies once because she left them in the bathroom when I was using it.